Microfabricated fluid pump

ABSTRACT

A microfabricated fluid pump is formed in a multilayer substrate by etching a plurality of shallow and deep wells into the layers, and then joining these wells with voids formed by anisotropic etching. The voids define a flexible membrane over the substrate which deforms when a force is applied. The force may be provided by an embedded layer of piezoelectric material. Embedded strain gauges may allow self-sensing and convenient, precise operational control.

CROSS REFERENCE TO RELATED APPLICATIONS

This non-provisional U.S. Patent Application is a Continuation-In-Part, claiming priority to U.S. patent application Ser. No. 15/477,593, which in turn claims priority to U.S. Provisional Patent Application 62/318,055, filed Apr. 4, 2016. These applications are incorporated by reference in their entireties.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

Not applicable.

STATEMENT REGARDING MICROFICHE APPENDIX

Not applicable.

BACKGROUND

This invention relates to a microfabricated pressure device formed on a multilayer substrate.

Microelectromechanical systems (MEMS) are very small moveable structures made on a substrate using lithographic processing techniques, such as those used to manufacture semiconductor devices. MEMS devices may be moveable actuators, sensors, valves, pistons, or switches, for example, with characteristic dimensions of a few microns to hundreds of microns. One example of a MEMS device is a microfabricated cantilevered beam, which may be used to switch electrical signals. Because of its small size and fragile structure, the movable cantilever may be enclosed in a cavity to protect it and to allow its operation in an evacuated environment. Therefore, upon fabrication of the moveable structure on a device wafer, the device wafer may be mated with a lid wafer, in which depressions have been formed to allow clearance for the structure and its movement. To maintain the vacuum over the lifetime of the device, a getter material may also be enclosed in the device cavity upon sealing the lid wafer against the device wafer.

Movable MEMS devices may include actuators, sensors and switches.nnMicrofabricated pressure sensors comprise a small but useful subset MEMS devices. Microfabricated sensors can be very sensitive to pressure changes, making them ideal for applications in which bulky machined sensors are not able to perform, or are too large, or consume too much power. Typical applications of integrated pressure sensors include microphones, biomedical instrumentation (e.g., blood and fluid pressure), vacuum sensing, wind-tunnel model instrumentation, automobile power and acceleration measurement, and even household electronics.

Generally, mechanical sensors are based on material changes caused by stress placed on a membrane or other flexible element. The most common and inexpensive type, is based on the piezoresistive effect, wherein the resistance of the piezoresistive element changes as a function of strain. Piezoresistors can be made of doped silicon or polysilicon. Polysilicon has better stability, avoids time- and temperature-variant p-n junctions, and can be used in operating temperatures up to 200° C. On the submillimeter scale of integrated devices, materials like silicon show very little or no fatigue, which is apparently a macroscale phenomenon. Thus integrated sensors can be flexed indefinitely, and have a long lifetime.

In addition to sensors based on the piezoresistive effect, there also exist high-precision sensors based on capacitive effect. A membrane is also used, with one plate of a capacitor mounted on the membrane and the other plate suspended above it, usually fabricated on a relatively inflexible material such as Pyrex glass. The deflection of the membrane changes the distance between the plates and thus changes the capacitance. Capacitors tend to be much less temperature and time variant than piezoresistors. Output of capacitive sensors is highly appropriate for switched-cap circuit design.

In many cases, the physical phenomenon that enabled the sensor to function, may also be used to cause an object to move, that is, the sensor can be made to function as an actuator. For example, PZT materials generate a voltage when placed under strain. Instead, by applying a voltage across a PZT layer, the layer may be forced to expand or contract as an actuator.

However, each of the aforementioned devices may be rather complex and expensive to manufacture. Accordingly, microfabricated, low cost pressure transducers have posed an unresolved problem.

SUMMARY

A microfabricated pressure device may use a membrane that deflects under a force. This deflection may then be measured any of a number of ways, for example optically, or piezoelectrically. In the embodiment described below, a PZT element may be used to drive the flexible membrane.

In the systems and methods described here, the microfabricated pressure device may be formed from a substrate of one or more materials with two embedded etch stop layers defining a top, center and bottom substrate part. The top substrate part may have a number of shallow wells extending through the top substrate part, and defining a perforated membrane in the top substrate part which is suspended over a first void. The top and center substrate parts may also have a plurality deep wells, the deep wells being deeper than the shallow wells and extending through the top and center substrate parts. The deeper wells may define a smaller unperforated membrane on the bottom substrate which is suspended over a second void, wherein the perforated and unperforated membranes form a force-to-pressure device.

A method for forming the microfabricated pressure device may include: providing a three layer substrate having a top, center and bottom layer, wherein the layers are separated by an upper and a lower etch stop, forming a plurality of holes through the top layer; forming a void below the top layer and above the bottom layer, but leaving at least one structure connecting the top and the bottom layers to form the pressure device.

The microfabricated fluid pump, cl 1 may include a multilayer substrate with an embedded layer of a piezoelectric material, the multilayer substrate having a top, center and bottom substrate part, the top substrate part, and having a first flexible membrane formed in the top substrate part which is deflected by the embedded PZT layer. The center substrate part may have a second flexible membrane disposed over a chamber in the bottom substrate part beneath the second flexible membrane. The first membrane may be connected to the second flexible membrane by a first rigid piston in the center substrate part, such that the first and second membranes are coupled together and whereby by the embedded PZT material forms the microfabricated fluid pump by deflecting the first and second membranes.

These and other features and advantages are described in, or are apparent from, the following detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

Various exemplary details are described with reference to the following figures, wherein:

FIG. 1 is a cross sectional schematic diagram of the microfabricated pressure transducer; and

FIG. 2 is a plan view of the microfabricated pressure transducer.

FIG. 3 is a cross sectional schematic diagram of a microfabricated piezoelectric actuator.

FIG. 4 is a cross sectional schematic diagram of one embodiment of a microfabricated fluid pump;

FIG. 5 is a plan view of the microfabricated fluid pump; and

FIG. 6 is a cross sectional schematic diagram of another embodiment of the microfabricated fluid pump.

It should be understood that the drawings are not necessarily to scale, and that like numbers may refer to like features.

DETAILED DESCRIPTION

In some of the systems and methods described herein may make use of a multilayer substrate, wherein three layers making up the substrate are separated by two etch stop layers, an upper etch stop layer and a lower etch stop layer. The etch stops may be, for example, an oxide of metal. The etch stops may be formed by, for example, the repetitive bonding of oxidized silicon wafers and appropriate grinding and polishing. Alternatively, the top substrate layer may be a glass, for example a borosilicate, that is anodically bonded to the center substrate. In that case the substrate itself would also include the etch stop on the top surface, the sidewalls; and the top buried etch stop all at once.

The bottom substrate may also alternatively be a glass, for example again a borosilicate glass, that is anodically bonded to the center substrate. In that case the substrate itself would also include the etch stop on the bottom surface.

Generally, the multilayer substrate may comprise various materials, each separated from the others by an etch stop material, a material that etches at a slower rate, or not at all, compared to the surrounding material. The method may include providing a multilayer substrate having a top, center and bottom layer, wherein the layers are separated by top and bottom etch stop layers, forming a plurality of holes through the top layer and top etch stop layer, and forming a void below the top layer and top etch stop layer and above the bottom layer and bottom etch stop layer, but leaving at least one structure connecting the top and the bottom layers to form the pressure transducer.

In one embodiment described below, the multilayer substrate has three silicon layers, top layer 6, middle layer 8 and bottom layer 10. Each of the layers 6, 8 and 10 may be separated by a silicon dioxide etch stop layer, upper etch stop layer 16 and lower etch stop layer 18. A plurality of blind holes or wells may be etched into these layers as follows. The basic architecture is shown in the cross section of FIG. 1 and plan view of FIG. 2.

The shallow 12 and deep 14 wells are etched together through the top silicon substrate layer 6. The entire substrate is then oxidized to form the sidewall etch stops. The shallow and deep wells, 12 and 14 respectively, are patterned again and etched anisotropically through the upper etch stop 16 without hurting the sidewall etch stops and the newly formed oxide etch stop on top of the top substrate 6.

The deep wells 14 may be patterned and the center substrate layer 8 is etched all the way to the bottom etch stop. An isotropic XeF₂ release etch may be performed that attacks the center substrate 8. The etch progresses radially from the ends of the shallow wells 12, and cylindrically from the deep wells 14; ultimately merging and creating a larger membrane on the top substrate and a smaller membrane on the bottom substrate. The etch may have to be stopped before the radial etches reach the bottom surface to ensure that the bottom membrane is smaller in size. By choosing the location and count of the wells a center “piston” like connecting structure 13 remains at the center substrate 8, connecting the top and bottom substrates, 6 and 10, and forming the transducer function. The connecting structure 13 may connect the top 6 and the bottom layer 10 to form the pressure transducer.

The multilayer substrate may be comprised of silicon, glass, polymers or metals; or a combination thereof. The etch stop layers may be comprised of thermal oxide or a metal. The sidewall etch stop layers may be comprised of thermal oxide or a CxFy polymer, wherein x and y are independent integers. The isotropic etchant may be comprised of XeF₂ gas, KOH, SF₆ plasma (if the substrates are Silicon), HF (if the substrates are glass), oxygen plasma (if the substrates are polymers).

In another embodiment, the microfabricated pressure transducer 2 may comprise an etch stop on top of the top substrate; the top substrate having a number of holes called shallow wells, which are passivated on the sidewalls and which breached the top etch stop; the top and center substrate having a number of holes called deep wells, which are passivated on the sidewalls only in the region of the top substrate; the center substrate having furthermore a larger void as a result of an isotropic etch that connects all wells with each other on the top part of the center substrate; but where only the deep wells are connected on the bottom part of the center substrate; thus creating a larger perforated membrane on the top substrate and a smaller unperforated membrane on the bottom substrate, which are optionally be connected by a piston like structure out of the center substrate and therefore form a force-to-pressure transducer 2.

The systems and methods described herein may be particularly applicable to systems needing a compact, inexpensive pressure transducer. However, they may also be applicable to any integrated circuit formed on a device wafer and encapsulated with a lid wafer.

Accordingly, a microfabricated pressure transducer has been described, which includes a substrate of one or more materials with two embedded etch stop layers defining a top, center and bottom substrate part, the top substrate part having a number of shallow wells extending through the top substrate part, and defining a perforated membrane in the top substrate part which is suspended over a first void. The top and center substrate parts may also have a plurality deep wells, the deep wells being deeper than the shallow wells and extending through the top and center substrate parts, and defining a smaller unperforated membrane on the bottom substrate which is suspended over a second void, wherein the perforated and unperforated membranes form a force-to-pressure transducer.

The shallow wells may be passivated on the sidewalls which breached the top etch stop. The deep wells are passivated on the sidewalls only in the region of the top substrate. The center substrate part may have a void that connects the shallow and the deeper wells with each other on the top part and the center substrate parts. The deep wells may be connected on the center substrate part. The shallow wells may define the larger perforated membrane on the top substrate. The deeper wells may define the smaller unperforated membrane on the bottom substrate. The membranes may be connected by a piston structure in the center substrate part, thereby forming the force-to-pressure transducer.

The substrate parts may be comprised of at least one of silicon, glass, polymers, metals, and combinations thereof. The embedded etch stop layers may be comprised of thermal oxide, metal or a metal oxide. The sidewalls on the etch stop layers may be comprised of at least one of a thermal oxide and a C_(x)F_(y) polymer, wherein x and y are two different integers. The wells may be formed by an isotropic etchant, and may be spaced radially around a center point, with the shallower wells located at a larger radius than the deeper wells.

The isotropic etchant may comprise at least one of XeF₂ gas, KOH, SF₆ plasma, HF, and oxygen plasma. The perforated membrane may include about 4 shallower wells and about 10 to about 15 deeper wells. The anisotropic etchant may comprise at least one of XeF₂ gas, KOH, SF₆ plasma, HF, and oxygen plasma. The perforated membrane includes about 4 shallower wells and about 10 to about 15 deeper wells.

Further, a method has been disclosed for forming a microfabricated pressure transducer. The method may include providing a multilayer substrate having a top, center and bottom layer, wherein the layers are separated by top and bottom etch stop layers, forming a plurality of holes through the top layer and top etch stop layer, and forming a void below the top layer and top etch stop layer and above the bottom layer and bottom etch stop layer, but leaving at least one structure connecting the top and the bottom layers to form the pressure transducer.

Within this method, the holes may comprise a plurality of shallow wells formed through the top layer. The method may further include passivating at least the top substrate to form sidewall etch stops without passivating an interface to the second layer, continuing to etch a subset of the shallow wells anisotropically through most or all of the center substrate to form deep wells. The method may further include etching the center layer isotropically down and outward from the wells to create a membrane on the top layer and a membrane on the bottom layer, and stopping the isotropic etch so that the etch front from the shallow wells does not contact the bottom membrane thus making the top membrane larger than the bottom membrane. The method may further include arranging the wells so that some of them are spaced sufficiently to surround one or several future piston, and stopping the isotropic etch so that the etch fronts from the sufficiently spaced wells do not meet and thus forms a piston-like connection between the top membrane and bottom membrane.

The method may further include etching the center layer to form a void that connects the shallow and the deeper wells with each other on the top part and the center substrate parts. The deep wells may be connected on the center substrate part. The shallow wells may define the larger perforated membrane on the top substrate. The deeper wells may define the smaller unperforated membrane on the bottom substrate.

The three layer substrate may comprise silicon, glass, polymers, metals and a combination thereof, wherein the etch stops may comprise at least one of a thermal Oxide or a CxFy polymer, and wherein the isotropic etch uses at least one of XeF₂ gas, KOH, SF₆ plasma, HF, and oxygen plasma.

In another embodiment, the transducer shown in FIG. 1 may be provided with an embedded piezoelectric layer 124, which may render the structure an active device. With PZT layer 124, the device 3 may become a fluid pump or fluid actuator. This embodiment is shown in FIG. 3. Among the properties of PZT materials is that they develop a voltage across the material when they are deformed. Using the embedded layer of PZT, and actuator 3 may be formed using this same basic architecture as the transducer 2.

As before, the multilayer substrate may have three silicon layers, a top layer 6, middle layer 8 and bottom layer 120. Each of the layers 6, 8 and 120 may be separated by a silicon dioxide etch stop layer, upper etch stop layer 16 and lower etch stop layer 18.

However, between the top layer 6 and middle layer 8, there may additionally be a layer of PZT material 124. This PZT layer 124 may cover the entire lateral extent of the multilayer substrate, that is, during wafer level processing, the PZT may form a continuous film extending over the whole area of the multilayer substrate. Accordingly, when a voltage is applied across the PZT, the PZT layer may deflect up and down in the direction shown by the arrow in FIG. 3. Since the layer 6 and diaphragm 120 are thin and flexible, the motion of the PZT 124 is coupled to the flexible diaphragm 120 by the piston 13. Therefore, the movement of the PZT 124 may cause a movement of the flexible diaphragm 120.

A plurality of blind holes or wells may be etched into these layers as follows. The shallow 12 and deep 14 wells may be etched together through the top silicon substrate layer 6. The entire substrate may then oxidized to form the sidewall etch stops. The shallow and deep wells, 12 and 14 respectively, are patterned again and etched anisotropically through the upper etch stop 16 without hurting the sidewall etch stops and the newly formed oxide etch stop on top of the top substrate 6.

The deep wells 14 may be patterned and the middle substrate layer 8 may be etched all the way to the bottom etch stop 18. An isotropic XeF₂ release etch is performed that attacks the middle substrate 8. The etch progresses radially from the ends of the shallow wells 12, and cylindrically from the deep wells 14; ultimately merging and creating a larger membrane on the top substrate and a smaller membrane on the bottom substrate, and void between them. The etch may have to be stopped before the radial etches reach the bottom surface to ensure that the bottom membrane is smaller in size. By choosing the location and count of the wells, a center “piston” like connecting structure 13 remains at the center substrate 8, connecting the top and bottom substrates, 6 and 120, and forming the PZT actuator 3 functionally. Accordingly, The piston connecting structure 13 may connect the top 6, the middle layer 8 and bottom membrane layers 120 to form the actuator 3.

The multilayer substrate may be comprised of silicon, glass, polymers or metals; or a combination thereof. The etch stop layers may be comprised of thermal oxide or a metal. The sidewall etch stop layers may be comprised of thermal oxide or a CxFy polymer, wherein x and y are independent integers. The isotropic etchant may be comprised of XeF₂ gas, KOH, SF₆ plasma (if the substrates are Silicon), HF (if the substrates are glass), oxygen plasma (if the substrates are polymers).

The actuator 3 shown in FIG. 3 may be combined with a pair of input and output fluid valves formed in yet another substrate to form a microfabricated pump, The actuator and valves, along with a quantity of fluid, may form an integrated, microfabricated fluid pump 4, and this integrated, microfabricated fluid pump 4 is shown in FIG. 4. Comparison of FIG. 4 to FIG. 1 and FIG. 3 shows many similarities, but important differences.

Once again, the multilayer substrate may have three silicon layers, a top layer 6, middle layer 8 and bottom diaphragm layer 120. Each of the layers 6, 8 and 120 may be separated by a silicon dioxide etch stop layer, upper etch stop layer 16 and lower etch stop layer 18.

As before, between the top layer 6 and middle layer 8, there may additionally be a layer of PZT material 124. This PZT layer 124 may cover the entire lateral extent of the multilayer substrate, that is, during wafer level processing, the PZT may form a continuous film extending over the whole area of the multilayer substrate. Accordingly, when a voltage is applied across the PZT, the PZT layer may deflect up and down in the direction shown by the arrow in FIG. 4. Since the bottom diaphragm 120 is thin and flexible, the motion of the PZT 124 is coupled to the flexible diaphragm 120 by the piston 130. Therefore, the movement of the PZT 124 may cause a movement of the flexible diaphragm 120. This may provide the pumping capability for the integrated, microfabricated fluid pump 4.

To make the fluid pump structure 4, a plurality of blind holes or wells may again be etched into these layers as follows. The shallow 12 and deep 14 wells may be etched together through the top silicon substrate layer 6. The entire substrate may then oxidized to form the sidewall etch stops. The shallow and deep wells, 12 and 14 respectively, are patterned again and etched anisotropically through the upper etch stop 16 without hurting the sidewall etch stops and the newly formed oxide etch stop on top of the top substrate 6.

The deep wells 14 may be patterned and the middle substrate layer 8 may be etched all the way to the bottom etch stop. An isotropic XeF₂ release etch is performed that attacks the center substrate 8. The etch progresses radially from the ends of the shallow wells 12, and cylindrically from the deep wells 14; ultimately merging and creating a larger membrane on the top substrate and a smaller membrane on the bottom substrate. The etch may have to be stopped before the radial etches reach the bottom surface to ensure that the bottom membrane is smaller in size. By choosing the location and count of the wells a center “piston” like connecting structure 130 remains at the middle substrate 8, connecting the top and bottom layers, 6 and 120, and forming the PZT actuator 3. function. The piston connecting structure 130 may connect the top 6 and the bottom layer 120 to form the pumping mechanism.

As is true of many pumps, an input valve and an output valve may allow the fluid to flow in response to the pressure changes provided by the moving flexible membrane or diaphragm 120. The inlet valve 150 may be functionally and structurally very similar to outlet valve 160. Inlet valve 150 may have a valve cover or flap 154 that is prestressed against a valve seat 152, so as to seal the passage between the reservoir 170 and the pumping chamber 140. It should be understood that the term “chamber” is used interchangeably with the term “void” to refer to a space formed in structure that may be intermittently filled with a fluid. The pumping pressure needed to open the inlet valve 150 and the outlet valve 160 may be in excess of the prestress pressure exerted by the valve flap against the valve seat.

Prestressing of the valve cover 154 may be accomplished by depositing the material of the valve cover at high temperature or high pressure or in the presence of an electric field, or by alloying the material with another component which imparts stress. The prestress may be applied during bonding. The spacing between valve seat and valve membrane may be less than the spacing between the bond lines. Accordingly, the two wafers may be aligned and brought into contact. At that moment the membrane may become prestressed

When a voltage is applied to the PZT layer 124, the layer will expand as a function of voltage, flexing upward. Since the PZT layer is coupled by the piston 130 to the flexible membrane 120, this movement will drive the flexible membrane 120 up. When the membrane 120 is deflected upward, that will increase the size of the pumping chamber 140, lowering the pressure therein. When the pressure is reduced below the threshold set by the prestressing of the inlet valve, 150, the inlet valve will open, allowing fluid to flow from the fluid reservoir 170 into the pumping chamber through the valve 150.

The PZT layer 124 and flexible membrane 120 will then reverse direction, and the membrane 120 will move downward, reducing the size of the pumping chamber 140, and thus raising the pressure therein. When the pressure differential exceeds the prestress of the outlet valve 160, the outlet valve 160 will open, allowing fluid to flow from the pumping chamber 140 to the output 180.

FIG. 5 is a plan view of the integrated, microfabricated pump 4. Shown in FIG. 4 is the input reservoir 170, which holds the fluid, the input valve 150, the piston 130, pumping chamber 140, output valve 160 and output 180. As described above, when a voltage is place across the PZT layer 124, the material will expand, flexing upward. The piston 130 connecting the PZT layer 124 to the flexible membrane 120 will drive the membrane 120 upward as well, increasing the volume of the pumping chamber 140. This will lower the pressure in the pumping chamber 140 until the input valve opens, allowing fluid to flow into the pumping chamber 140. When the membrane relaxes back downward, it will force the output valve 160 to open, driving the fluid into the output 180.

FIG. 6 is a cross sectional view of another embodiment of an integrated, microfabricated pump 6. In this embodiment, a set of integrated sensors can provide information about the performance of the integrated, microfabricated pump 6. There may be several strain gauges 132, 142 and 152 disposed adjacent to the pumping piston 130. Each strain gauge 132, 142 and 152 may have associated with it a piston 140, 130 and 150, which connects the strain gauge to a respective flexible membrane 122, 124 and 126.

The input strain gauge 142 may measure a deflection of its associated flexible membrane 122. When the pump piston 130 rises in response to an applied voltage, this may reduce the pressure in the pumping chamber 140 until the input valve 150 opens. The opening of the input valve 150 will allow fluid to flow from the input reservoir 170. The opening of input valve 150 will cause an abrupt pressure differential to be applied to the flexible membrane 160. The strain gauge 162 will respond to the movement of the associated membrane 160, to produce a signal indicative of the motion of associated membrane 160 and opening of input valve 150.

Similarly, when the pump piston 130 moves downward, it will increase the pressure in the pumping chamber 140 until the output valve 160 opens. When this valve opens, fluid will flow from the pumping chamber to the outlet 180. The movement of this fluid will cause a movement of associated flexible member 152 by piston 150. This motion is transmitted by piston 150 to strain gauge 152. The strain gauge will produce a signal indicative of this operation.

A third strain gauge 132 may be disposed on the pumping piston 130, to produce a signal indicative of the motion of the pumping piston 130.

Strain gauges 132, 142 and 152 may be fabricated by ion implantation of a region of the silicon substrate. Details as to the manufacture of such microfabricated self-sensing strain gauges may be found in U.S. application Ser. No. 15/477,593, filed Apr. 3, 2017. This application is incorporated by reference in its entirety.

Accordingly, using the self-sending integrated microfabricated fluid pump 5, the pump 5 operation may be precisely controlled by using the strain sensors in a feedback loop. The sensors can also alert the operator of malfunctions, such as the run-dry condition or the clogging of a microchannel.

Accordingly, a microfabricated fluid pump is described, which can be integrated on a substrate with self-sensing, fluid valves and fluid reservoirs. The microfabricated fluid pump may include a multilayer substrate with an embedded layer of a piezoelectric material, the multilayer substrate having a top, center and bottom substrate part, the top substrate part, and having a first flexible membrane formed in the top substrate part which is deflected by the embedded PZT layer. The center substrate may have a second flexible membrane disposed over a chamber in the bottom substrate part beneath the second flexible membrane, wherein the first membrane is connected to the second flexible membrane by a first rigid piston in the center substrate part, such that the first and second membranes are coupled together and whereby by the embedded PZT material forms the microfabricated fluid pump by deflecting the first and second membranes.

In the microfabricated fluid pump, the first membrane may be perforated by a plurality of holes and the second membrane is unperforated, wherein the chamber is shaped to accommodate the movement of the first rigid piston. An inlet valve and an outlet valve may allow a fluid to flow into and out of the chamber from an inlet and outlet port. The inlet valve and the outlet valve may be passive, opening and closing as a result of fluid pressure generated by the deflected membranes. The inlet valve and the outlet valve may be prestressed, such that they are pressed against a stop when no fluid pressure is applied.

A second and a third rigid pistons may be disposed laterally adjacent to the first rigid piston, and the second and third rigid pistons may be couple to strain gauges to measure a signal indicative of the performance of the microfabricated fluid pump. The strain gauges may be coupled to a feedback loop that operates the microfabricated fluid pump.

The substrate parts may be comprised of at least one of silicon, glass, polymers, metals, and combinations thereof, and the embedded piezoelectric layer comprises lead zirconate titanate Pb[Zr_(x)Ti_(1-x)]O₃.

The embedded piezoelectric layer may be substantially intact and sandwiched between two conductors, which apply a voltage across the embedded piezoelectric layer. The embedded piezoelectric layer may be substantially intact and extend across the entire lateral dimension of the device. The embedded piezoelectric layer may extend across the entire lateral dimension of a total, unseparated fabrication wafer on which a plurality of microfabricated fluid pumps of claim 1 are formed.

A method for forming a microfabricated fluid pump is also disclosed. The method may include providing a multilayer substrate having a top, center and bottom parts, providing an embedded layer of a piezoelectric material, between the top and center substrate parts, forming a first flexible membrane in the top layer and the layer of piezoelectric material, and forming a second flexible membrane in the center part, and a chamber in the bottom part beneath the second flexible membrane, but leaving at least one first rigid piston coupling the first and second flexible membranes to form the fluid pump when a voltage is applied across the piezoelectric layer, such that the first and second membranes are deflected together by the embedded PZT material to form the microfabricated fluid pump.

The method may further include forming a plurality of holes in the first flexible membrane to form a perforated membrane, forming a chamber in another substrate, wherein the chamber is shaped to accommodate the movement of the piston, and adhering the substrate with the chamber to the multilayer substrate to form the microfabricated fluid pump. The method may further include forming an inlet valve and an outlet valve which allow a fluid to flow into and out of the chamber from an inlet and outlet port. The inlet valve and the outlet valve may be passive, and open and close as a result of fluid pressure generated by the deflected membranes. The inlet valve and the outlet valve may be prestressed, such that they are pressed against a stop when no fluid pressure is applied.

The method may further include forming a second and third rigid piston structures laterally adjacent to the first rigid piston. The method may further include forming strain sensors in the second and third rigid piston structures, wherein the strain sensors measure the deflection of the perforated membrane, and thus the fluid pressure in the inlet and outlet port.

In the method, the embedded piezoelectric layer may be substantially intact and extends across the entire lateral dimension of the device. The embedded piezoelectric layer may be substantially intact and extend across the entire lateral dimension of a wafer on which a plurality of microfabricated fluid pumps are formed.

While various details have been described in conjunction with the exemplary implementations outlined above, various alternatives, modifications, variations, improvements, and/or substantial equivalents, whether known or that are or may be presently unforeseen, may become apparent upon reviewing the foregoing disclosure. Accordingly, the exemplary implementations set forth above, are intended to be illustrative, not limiting. 

What is claimed is:
 1. A microfabricated fluid pump, comprising: a multilayer substrate with an embedded layer of a piezoelectric material, the multilayer substrate having a top, center and bottom substrate part, the top substrate part, and having a first flexible membrane formed in the top substrate part which is deflected by the embedded PZT layer; the center substrate part having a second flexible membrane disposed over a chamber in the bottom substrate part beneath the second flexible membrane, wherein the first membrane is connected to the second flexible membrane by a first rigid piston in the center substrate part, such that the first and second membranes are coupled together and whereby by the embedded PZT material forms the microfabricated fluid pump by deflecting the first and second membranes.
 2. The microfabricated fluid pump of claim 1, wherein the first membrane is perforated by a plurality of holes and the second membrane is unperforated, wherein the chamber is shaped to accommodate the movement of the first rigid piston.
 3. The microfabricated fluid pump of claim 2, wherein an inlet valve and an outlet valve allow a fluid to flow into and out of the chamber from an inlet and outlet port.
 4. The microfabricated fluid pump of claim 3, wherein the inlet valve and the outlet valve are passive, opening and closing as a result of fluid pressure generated by the deflected membranes.
 5. The microfabricated fluid pump of claim 4, wherein the inlet valve and the outlet valve are prestressed, such that they are forced against a stop when no fluid pressure is applied.
 6. The microfabricated fluid pump of claim 4, wherein a second and third rigid pistons are disposed laterally adjacent to the first rigid piston, and the second and third rigid pistons are couple to strain gauges to measure a signal indicative of the performance of the microfabricated fluid pump.
 7. The microfabricated fluid pump of claim 6, wherein the strain gauges are coupled to a feedback loop that operates the microfabricated fluid pump.
 8. The microfabricated fluid pump of claim 1, wherein the substrate parts are comprised of at least one of silicon, glass, polymers, metals, and combinations thereof, and the embedded piezoelectric layer comprises lead zirconate titanate Pb[Zr_(x)Ti_(1-x)]O₃.
 9. The microfabricated fluid pump of claim 1, wherein the embedded piezoelectric layer is substantially intact and sandwiched between two conductors, which apply a voltage across the embedded piezoelectric layer.
 10. The microfabricated fluid pump of claim 1, wherein the embedded piezoelectric layer is substantially intact and extends across the entire lateral dimension of the device.
 11. The microfabricated fluid pump of claim 1, wherein the embedded piezoelectric layer extends across the entire lateral dimension of a total, unseparated fabrication wafer on which a plurality of microfabricated fluid pumps of claim 1 are formed.
 12. A method for forming a microfabricated fluid pump, comprising: providing a multilayer substrate having a top, center and bottom parts; providing an embedded layer of a piezoelectric material, between the top and center substrate parts; forming a first flexible membrane in the top layer and the layer of piezoelectric material; and forming a second flexible membrane in the center part, and a chamber in the bottom part beneath the second flexible membrane, but leaving at least one first rigid piston coupling the first and second flexible membranes to form the fluid pump when a voltage is applied across the piezoelectric layer, such that the first and second membranes are deflected together by the embedded PZT material to form the microfabricated fluid pump.
 13. The method of claim 12, further comprising: forming a plurality of holes in the first flexible membrane to form a perforated membrane; forming a chamber in another substrate, wherein the chamber is shaped to accommodate the movement of the piston; and adhering the substrate with the chamber to the multilayer substrate to form the microfabricated fluid pump.
 14. The method of claim 13, further comprising forming an inlet valve and an outlet valve which allow a fluid to flow into and out of the chamber from an inlet and outlet port.
 15. The method of claim 14, wherein the inlet valve and the outlet valve and passive, and open and close as a result of fluid pressure generated by the deflected membranes.
 16. The method of claim 14, wherein the inlet valve and the outlet valve are prestressed, such that they are pressed against a stop when no fluid pressure is applied.
 17. The method of claim 12, further comprising: forming a second and third rigid piston structures laterally adjacent to the first rigid piston.
 18. The method of claim 17, further comprising forming strain sensors in the second and third rigid piston structures, wherein the strain sensors measure the deflection of the perforated membrane, and thus the fluid pressure in the inlet and outlet port.
 19. The method of claim 12, wherein the embedded piezoelectric layer is substantially intact and extends across the entire lateral dimension of the device.
 20. The microfabricated fluid pump of claim 1, wherein the embedded piezoelectric layer is substantially intact and extends across the entire lateral dimension of a wafer on which a plurality of microfabricated fluid pumps of claim 1 are formed. 